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Date: Mon, 4 Dec 2017 14:37:44 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Wang Nan <wangnan0@...wei.com>
Cc: linux-kernel@...r.kernel.org, kan.liang@...el.com, acme@...nel.org,
jolsa@...hat.com, kernel-team@....com
Subject: Re: [PATCH v2 6/8] perf mmap: Fix perf backward recording
Hi,
On Sun, Dec 03, 2017 at 02:00:42AM +0000, Wang Nan wrote:
> perf record backward recording doesn't work as we expected: it never
> overwrite when ring buffer full.
>
> Test:
>
> (Run a busy printing task background like this:
>
> while True:
> print 123
>
> send SIGUSR2 to perf to capture snapshot.)
>
> # ./perf record --overwrite -e raw_syscalls:sys_enter -e raw_syscalls:sys_exit --exclude-perf -a --switch-output
> [ perf record: dump data: Woken up 1 times ]
> [ perf record: Dump perf.data.2017110101520743 ]
> [ perf record: dump data: Woken up 1 times ]
> [ perf record: Dump perf.data.2017110101521251 ]
> [ perf record: dump data: Woken up 1 times ]
> [ perf record: Dump perf.data.2017110101521692 ]
> ^C[ perf record: Woken up 1 times to write data ]
> [ perf record: Dump perf.data.2017110101521936 ]
> [ perf record: Captured and wrote 0.826 MB perf.data.<timestamp> ]
>
> # ./perf script -i ./perf.data.2017110101520743 | head -n3
> perf 2717 [000] 12449.310785: raw_syscalls:sys_enter: NR 16 (5, 2400, 0, 59, 100, 0)
> perf 2717 [000] 12449.310790: raw_syscalls:sys_enter: NR 7 (4112340, 2, ffffffff, 3df, 100, 0)
> python 2545 [000] 12449.310800: raw_syscalls:sys_exit: NR 1 = 4
> # ./perf script -i ./perf.data.2017110101521251 | head -n3
> perf 2717 [000] 12449.310785: raw_syscalls:sys_enter: NR 16 (5, 2400, 0, 59, 100, 0)
> perf 2717 [000] 12449.310790: raw_syscalls:sys_enter: NR 7 (4112340, 2, ffffffff, 3df, 100, 0)
> python 2545 [000] 12449.310800: raw_syscalls:sys_exit: NR 1 = 4
> # ./perf script -i ./perf.data.2017110101521692 | head -n3
> perf 2717 [000] 12449.310785: raw_syscalls:sys_enter: NR 16 (5, 2400, 0, 59, 100, 0)
> perf 2717 [000] 12449.310790: raw_syscalls:sys_enter: NR 7 (4112340, 2, ffffffff, 3df, 100, 0)
> python 2545 [000] 12449.310800: raw_syscalls:sys_exit: NR 1 = 4
>
> Timestamps are never change, but my background task is a dead loop, can
> easily overwhelme the ring buffer.
>
> This patch fix it by force unsetting PROT_WRITE for backward ring
> buffer, so all backward ring buffer become overwrite ring buffer.
>
> Test result:
>
> # ./perf record --overwrite -e raw_syscalls:sys_enter -e raw_syscalls:sys_exit --exclude-perf -a --switch-output
> [ perf record: dump data: Woken up 1 times ]
> [ perf record: Dump perf.data.2017110101285323 ]
> [ perf record: dump data: Woken up 1 times ]
> [ perf record: Dump perf.data.2017110101290053 ]
> [ perf record: dump data: Woken up 1 times ]
> [ perf record: Dump perf.data.2017110101290446 ]
> ^C[ perf record: Woken up 1 times to write data ]
> [ perf record: Dump perf.data.2017110101290837 ]
> [ perf record: Captured and wrote 0.826 MB perf.data.<timestamp> ]
> # ./perf script -i ./perf.data.2017110101285323 | head -n3
> python 2545 [000] 11064.268083: raw_syscalls:sys_exit: NR 1 = 4
> python 2545 [000] 11064.268084: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
> python 2545 [000] 11064.268086: raw_syscalls:sys_exit: NR 1 = 4
> # ./perf script -i ./perf.data.2017110101290 | head -n3
> failed to open ./perf.data.2017110101290: No such file or directory
> # ./perf script -i ./perf.data.2017110101290053 | head -n3
> python 2545 [000] 11071.564062: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
> python 2545 [000] 11071.564064: raw_syscalls:sys_exit: NR 1 = 4
> python 2545 [000] 11071.564066: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
> # ./perf script -i ./perf.data.2017110101290 | head -n3
> perf.data.2017110101290053 perf.data.2017110101290446 perf.data.2017110101290837
> # ./perf script -i ./perf.data.2017110101290446 | head -n3
> sshd 1321 [000] 11075.499473: raw_syscalls:sys_exit: NR 14 = 0
> sshd 1321 [000] 11075.499474: raw_syscalls:sys_enter: NR 14 (2, 7ffe98899490, 0, 8, 0, 3000)
> sshd 1321 [000] 11075.499474: raw_syscalls:sys_exit: NR 14 = 0
> # ./perf script -i ./perf.data.2017110101290837 | head -n3
> python 2545 [000] 11079.280844: raw_syscalls:sys_exit: NR 1 = 4
> python 2545 [000] 11079.280847: raw_syscalls:sys_enter: NR 1 (1, 12cc330, 4, 7fc237280370, 7fc2373d0700, 2c7b0)
> python 2545 [000] 11079.280850: raw_syscalls:sys_exit: NR 1 = 4
>
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> ---
> tools/perf/util/evlist.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 68c1f95..bb70aef 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -799,7 +799,7 @@ perf_evlist__should_poll(struct perf_evlist *evlist __maybe_unused,
> }
>
> static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
> - struct mmap_params *mp, int cpu_idx,
> + struct mmap_params mp, int cpu_idx,
> int thread, int *_output, int *_output_backward)
> {
> struct perf_evsel *evsel;
> @@ -824,6 +824,7 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
> if (evlist->bkw_mmap_state == BKW_MMAP_NOTREADY)
> perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING);
> }
> + mp.prot &= ~PROT_WRITE;
> }
>
> if (evsel->system_wide && thread)
> @@ -838,7 +839,7 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
> if (*output == -1) {
> *output = fd;
>
I still prefer updating mp->prot based on evsel->attr.write_backward
here (instead of passing mp as value). It'd create a minimal change.
Thanks,
Namhyung
> - if (perf_mmap__mmap(&maps[idx], mp, *output) < 0)
> + if (perf_mmap__mmap(&maps[idx], &mp, *output) < 0)
> return -1;
> } else {
> if (ioctl(fd, PERF_EVENT_IOC_SET_OUTPUT, *output) != 0)
> @@ -890,7 +891,7 @@ static int perf_evlist__mmap_per_cpu(struct perf_evlist *evlist,
> true);
>
> for (thread = 0; thread < nr_threads; thread++) {
> - if (perf_evlist__mmap_per_evsel(evlist, cpu, mp, cpu,
> + if (perf_evlist__mmap_per_evsel(evlist, cpu, *mp, cpu,
> thread, &output, &output_backward))
> goto out_unmap;
> }
> @@ -917,7 +918,7 @@ static int perf_evlist__mmap_per_thread(struct perf_evlist *evlist,
> auxtrace_mmap_params__set_idx(&mp->auxtrace_mp, evlist, thread,
> false);
>
> - if (perf_evlist__mmap_per_evsel(evlist, thread, mp, 0, thread,
> + if (perf_evlist__mmap_per_evsel(evlist, thread, *mp, 0, thread,
> &output, &output_backward))
> goto out_unmap;
> }
> --
> 2.10.1
>
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